During the latter part of the nineteenth century stereoscopic print viewers were in wide use, mostly with photographs produced professionally. Cameras available for general use were far from satisfactory. Most print viewers were large and not well suited for use outside of home or school. More compact viewers had shortcomings in performance.
In order to take fullest advantage of my stereoscopic cameras, U.S. Pat. No. 3,045,572, I have invented this viewer for optimum performance, compact, and convenient, which can be produced at low cost.
The most simple print viewer requires each print to be no wider than the minimum interoccular distance of users. This print size, less than 2 1/2 inches wide, limits the important social interaction between persons examining the prints in two dimensions, without a viewer,
According to historical references, the original stereoscope without mirrors was invented by Brewster. Oliver Wendall Holmes invented using lenses off-center, with the lens centers outward from the viewer center, to act as prisms, permiting viewing of prints somewhat wider than 1/2 inches. I cannot find patents on either of these viewers, Perhaps none were issued. The earliest patent I could find to mention the prismatic system is U.S. Pat. No. 174,893, Mar. 21, 1876, which states "These glasses are known as prismatic lenses, that is, they are double convex lenses, divided transversely, and so set that their thin edges are toward each other.",The drawing barely shows this in the patent. In U.S. Pat. No. 88,769, Mar. 27, 1877 it states "the lenses are of usual character", and since the drawings clearly show the prismatic lenses, it can be assumed they were in general use at that early date.